Hi all,

Lately my house always suffer power trip randomly; e.g. not because of lightning or switch on appliance. Example; this morning around 4am power trip again.

MCB/ELCB did not trip; but the outside fuse near TNB meter blown. Always happened this way. Usually I replaced this fuse; but it will randomly happened again.

Any idea why it trip this way? And is it normal if I switch off MCB but TNB meter still show movement (very slow)?

have u report to TNB everytime the fuse blown? normally incoming problem before meter is under TNB responsibility, ask them to solve it.

outside meter fuse rating is 60ampere for single phase. basically fuse will blown when current overload.

Current overload from outside or inside?

Last time already called TNB, but they asked me to get a technician because probably due to faulty appliance or bad wiring inside the house. But after it happened again this morning; I'm not sure it originated from the house.

This morning, I off MCB; and right when I insert the new fuse it blows.

when you say you off MCB, is it the :

(A)


or

(B)

Both. In fact I switch all those in the MCB box.

i never had a problem with external fuse blown,
but i encountered a problem last month regarding my RCCB (the one in picture B).

power trip due to wallsocket faulty, but all MCB, RCCB, ELCB not tripped.
was puzzled at first, but when i tried turning ON/OFF the MCB & RCCB, the power is back on again.

it happened again afterwards, during a thunderstorm (and lightning),
no power due to lightning strike, but all MCB (picture A), RCCB & ELCB not tripped.

did some checking, and i assumed that my RCCB is faulty: there was no power in the house,
but the RCCB switch is in its 'ON" position (internal mechanism i guess).

changed my RCCB and it solved my problem, so far.

do you check your RCCB regularly (press the 'TEST' button to see if it can trip)?

No I didn't check the TEST button, will try it after I put back the fuse.

faulty earth cable maybe ?
or maybe the fusebox got cable short circuit ?

outside fuse cant blow unless the current masuk ur house...
but since u off all the fuse, still can blow , maybe its time to check back all then wiring between main fuse to your fuse box...

inb4, i main hentam pull out and plug in main fuse near meter when fixing my new house, never experience it getting blown...

if it works (the RCCB can trip using TEST button), then RCCB might not be at fault.
if it doesn't work, then why not try changing your RCCB first, and observe if the external fuse still blow afterwards.

like what MadhavanR mentioned, i also had the experience that normally the external fuse
can just cabut/replace to do anything to your main fuse box.. seldom that we'd have it getting blown (multiple times some more).

Which fuse? the one beside the meter?

- Your's is 3 phase or single phase
- What is usually turned on? like the incident this morning?

Forgot to add, I have already replaced everything in the MCB box after it happened the second time.

I think its single phase. Nothing unusual switched on.

since you've changed everything in the mains box,
then most likely there's something wrong with your house wiring
or probably the cable in-between the main lines - connected to your mains box.

is it a new house? are you the first owner/occupant?

If I am not mistaken, the fuse beside the meter is slow blow fuse (if its the one beside the meter), it take hell lots of current or high spark of voltage to blow that fused (shorting is one of the method). Or long use of overloading to blow that fused (Long as in > few second).

<Assuming your internal wiring are working> your's situation, the outside fuse blow at random time and internal fused box not trip, and internal Main switch (also fused protected) not blow / trip. Could happen if somethings / animal move a loose wire in between the meter and fused box inside.

Yeah I think so too. Already discussed with electrician to install a new wire between meter and MCB.

Did you off all the MCB before insert the fuse?

What you can do is isolated the problem to find out where it happen.

Before insert the fuse again, off all the MCB. off the rccb and take out the main fuse beside the rccb.

If the main fuse doesn't blow, than return back the main fuse. Than the rccb. Than 1 by 1 ON back the mcb. Till the fuse blow again.

Than you can know where it happen.

Yes; already off all MCB. When inserting the new fuse, sparks come out and the fuse blow.

You're describing a direct short circuit (Live to Neutral).. If you're sure the DB isolator is off then the cable fault is between the kWh meter to the DB..

Have you had any renovation work done recently? Or anyone drive nails into walls ??

They might have accidentally driven a nail into the Live/Neutral cables thus blowing out your fuse..

If shorted, but not trip TS will be able to enjoy HIGH electric bill, but before that a fire may also happen if the fuse are not blow.

Something have shorted.. If not it won't spark. Perhaps someone stealing your electric, or internal got shorted. Check how fast your meter going (if LED is faster the blink mean high consumption, if analog you see it turn like F1)

Or did you do "creative" wiring to have your bill reduced?

I have no idea what you are talking about.. do you?

If the live is shorted with resistance it will have current drain, that mean energy used, if the heat build up it will have bbqing.

you're saying a slow thermal buildup short circuit as in the case of indirect conductivity (surface dust, liquid and conductive flesh)..


but Aeran typed "already off all MCB. When inserting the new fuse, sparks come out and the fuse blow" that describes an instantaneous short circuit..

Anyway the easiest way to check is to disconnect both ends of Live Neutral and check for continuity between the two..
If there's continuity then its a direct short..

Yes, and his problem maybe in between the meter and mcb main fuse/switch. That possible explain even after switch off all mcb it still have spark. Possible some shorting between there, or someone stealing electric, or maybe did some creative wiring to bypass meter.

yes.. So best thing is to get an electrician if not sure as we're talking mains electricity here and it can kill you..

Guys, finally can get electrician to come and see this morning. Will update later.

No; I'm not using any 'creative' wiring to bypass meter. Though previously I do notice the meter tend to spin a bit fast.

Hope you find the problem.

Update: Confirm wire between meter and MCB was shorted.

That is good to know you found the problem. Lucky it didn't catch fire. I hope the TNB bill won't go crazy, since is a temporary short / resistance shorted could eat up lots of energy.

Didn't you feel light or some of your equipment behaving? Assuming is resistance shorted, voltage into your house very likely will be way below 230v

Same problem at one of my properties. No trip at all but outside fuse near meter blown 4 times over a period of 2 months. Found out later that one external cable extended to a birdhouse was bitten by squirrel/mouse thus causing live and neutral shorted from time to time.

you are one cuckoo fella.. people say incoming live/neutral already confirm short blow fuse still say resistance short, talk voltage ?? Pls stop talking cock !!!

Already blow fuse means no more supply !! You talk what !!

If his house had fuse blow only sometime and not always is either a resistance short or expose short when movement happen. and If all MCB are trip are up Meter will not run, this only happen because of leakage due to lousy insulation or faulty meter, if leakage are major it will cause voltage drop. During my college time, i been working in factory and old house wiring and seen many of such cases.

Pls stop.. You can use your bullshit on some factory but not with me.. Please go home study your basic electrical 101 then come back and talk..

By right, the MCB should trip 1st.

Time to change the MCB.

It may not trip the main switch if happen between the meter and main switch . Most common happen with old houses with 3 phase meter at gate pillar when underground cable is damage.

Not TS case. But aeiou228 case.

MCB won't trip if the short circuit happen before the MCB incoming.

While aeiou228 case is after the MCB. Since the MCB have lower Amp rating than the fuse, it should trip 1st before the fuse.

Ok, if is extended from inside the MCB yes, if its extended from the meter will blow the main fuse..

This post has been edited by weikee: Jun 16 2016, 09:17 AM

The shorted cable has a dedicated MCB extended from the DB in house A and all the way to a birdhouse B. The cable shorted in between A and B.
Only realized cable shorted upon seeing a spark at the cable.
I did ask my electrician why there is no tripping but was told when live and neutral shorted, the MCB wouldn't trip but the main fuse blown instead. Can any sifu care to explain ?

Every DB will have one main fuse or some call it main breaker. There are many possible how your house cable is extend,
01) Extension/tapping before the main fuse
02) Extension/tapping after the main fuse.
03) Extension/tapping after the main fuse and one MCB.

<If all Circuit Breaker function as normal> and your Cable A & B are shorted
extension 01 method, only the incoming fuse beside meter will burned
extension 02 method, the main fuse will trip making entire house will have no electric
extension 03 method, usually is the prefer if current are not high. The individual MCB will trip first. This is also good if you want to totally shutdown the supply from outside.


You can test it out by trip the Main fuse in the DB Box. and if the birdhouse still have power mean is using method 01.

Thank you sir,
These are the info that I can gether.
1) when cable A to B shorted, the was a big spark, main fuse blown off and house A and birdhouse B no electricity.
2) before knowing the actual cause of the problem. wireman came replaced the main fuse in the morning but evening fuse blown again.
3) wireman disconnected the birdhouse cable from MCB in the DB, no more blown fuse but birdhouse B no electricity.
4) upon checking no wiring problem inside birdhouse B, I asked wireman to reconnect the birdhouse cable to MCB.
5) it lasted for a few days before the main fuse blown again. Replaced the fuse again without disconnecting the MCB for the birdhouse for further investigation.
6) break through came when a spark happened before my every eyes. A and B is about 40-50m apart and the extension outdoor cable is supported by cable pole and trees. The spark happened at a tree.
7) wireman fixed the exposed cable and no more blown fuse ever since.

So which extension method in this case?

MCB function is just like a fuse.

Fuse blow, you need to change. MCB trip, just need to reset back.

So the MCB should be able to trip. Since the MCB is 20A max trip. While the fuse is 63A blow.

Should ask the electrician to test it out the MCB is function properly or not. Change it if problem.



I do have many experience some plug point short. and trip the MCB. Main fuse doesn't blow. it should be in this way.

Do have experience some rare case, where the main fuse blow only. Where the shortcircuit Amp instant short is too high.

Can't give a firm answer base on your experience. #1 happen because incoming fuse are blow. That affect House A & B.

If you happen to be in that house, just try trip the main house Master switch inside your house. Check if your birdhouse still have electric. This will confirm of the birdhouse is tap before or after the Master switch. If is tap after the master switch, and your house master switch did not trip, you need to replace it as per ozak suggest. If is before the master switch that is normal behavior.

Thank you sirs.

I'm very sure if the master switch in house A tripped, the birdhouse no electricity also. Happened few times already.
Also, when wireman disconnected the birdhouse cable from the MCB inside the house A's DB, birdhouse house no electricity. When reconnected the cable to MCB, birdhouse got electricity.
The power supply of birdhouse is definitely tapped from DB of house A.

So in this case, the wireman was wrong to say that if live and neutral shorted (the cable between A and B), the MCB wouldn't trip but main fuse will blow instead ?

Based on your description, your main fuse may need to change. Did you replace correct rating fuse on the incoming? There is 60A, and 40A version. Same size but different Amp rating.

Just so you guys are clear on how a miniature circuit breaker works, the current travels through the bimetallic before it goes through magnetic coils tripping mechanism either of which will trip the device..

So for your scenario to happen..

the main fuse ampere rating must be much less than the mcb rating.. meaning as an example 40A HRC fuse(Kwh meter) wired to a 60A mcb (DB) (which is not the way to do wiring)..

An mcb in a DB must always trip before the HRC fuse..

Which brings up a doubt whether your wireman is sure of the protection devices ratings..

Yes, the wireman is wrong. If he know it, he will test it for you and recommend to change or not.

MCB Amp rating should be lower than the Fuse Amp rating. So the MCB will trip 1st.

Beter check your MCB any problem. Most of the time, I encounter the MCB is mechanical jam.

Ignore my rare case. It is just some rare experience that I experience before. But it do happen.

Mechanical can jam if the house DB flooded before and not replace.

Not just that.

Some is aging. If you always put it at ON for thousand yrs, and never trip it before, the mechanical will stuck there.

Some is quality issue. You know nowadays this MCB source from where la. Cheap is the issue. What I know is ABB still produce MCB locally. In subang.

In some case, the contact fuse together. Prevent it from trip.

Some is broken contact joint to the tripping mechanical. Result no contact.

This are some case that I encounter before. Normally I will CSI inside to see what happen.

here is 1 of the MCB component. This is the fuse tripping coil from my customer.

ABB Subang, (facing Kesas) no longer produce MCB for residential and commercial. All the low voltage MCB are build in China for many years already. The Subang factor are producing larger scale switchboard, I know, because my previous company I go there often and into their factor too.

This post has been edited by weikee: Jun 17 2016, 10:23 AM

Many yrs didn't heard their news.

All china now. Sigh!

since you mcb inside DB no trip means in between tnb supply to you db might be leak
to blow that 60a fuse the current must've flow to sumwhere.
most likely ground (thru anything i dunno) but it doesnt go thru ur DB since no mcb tripped.

infact i doubt your household will even draw 60a
this must be leak issue.

no.. Its classic short circuit.. Live / Neutral ... its the only way to blow a fuse.. any other type of fault will trip the breaker..

But how the wireman is missing it is beyond my understanding..

--- double post ---

This post has been edited by Richard: Jun 17 2016, 05:50 PM

Just some correction, ABB MCB was never produced in Malaysia. Those sold locally are from China factory, but the original Germany factory is still producing MCB, just not sold locally.